There have been numerous prior art analog to digital converters employing capacitors in their operation. A typical one is disclosed in U.S. Pat. No. 3,449,741 which was issued June 10, 1969 to M. W. Egerton, Jr., which patent discloses an analog to digital converter which employs a matched pair of capacitors as a quantum level generator. The matched pair of capacitors are initially charged to a reference voltage and then alternately switched in parallel and to ground to obtain a binarily decreasing staircase waveform. These decreasing increments of charge are sequentially added to a prior state stored voltage and compared with the analog sample to be coded. The result of this comparison determines whether the charge increment is retained or removed from the stored generated voltage.
U.S. Pat. No. 3,626,408 issued on Dec. 7, 1971 to R. L. Carbrey discloses a charge redistribution coder circuit. The Carbrey coder circuit also employs a matched pair of capacitors as a quantum level generator. The matched pair of capacitors are initially charged to a reference voltage and then alternately switched in parallel and to ground to obtain a binarily decreasing staircase waveform. These decreasing increments of charge are sequentially added to a prior state voltage stored on a third capacitor and compared with the analog sample to be coded. The result of this comparison determined whether this charge increment is to be added to a fourth capacitor which stores the cumulative coded result.
These prior art coder circuits all employ matched capacitors and charge redistribution techniques to sequentially generate a binarily decreasing staircase waveform which is added to a prior state voltage to match the analog sample voltage stored on a separate holding capacitor. These charge redistribution capacitors must be precisely matched to accurately generate the binarily decreasing staircase waveform. Capacitor mismatch is thus a major source of error in the operation of these prior art analog to digital converter circuits. Additionally, these coders operate sequentially and require n decision intervals to generate one n bit word. For wideband signals, such as video or multiplexed Pulse Amplitude Modulation signals, these prior art single bit coders may not operate with sufficient speed.
An alternative coding arrangement is the wave coding technique wherein n individual coding circuits are provided. The result of each individual bit decision is propagated to the subsequent stage for a decision therefore coding incoming signals n times faster than the above-mentioned successive approximation type coder which employs only one decision circuit. A typical prior art wave coder however, requires a number of parallel signal propagation paths which therefore requires a multiplicity of matched components.